Semi-transmissive liquid crystal display device and electronic apparatus

ABSTRACT

According to an aspect, a semi-transmissive liquid crystal display device includes a plurality of pixels arranged in a matrix, a plurality of reflective electrodes, a counter electrode facing the reflective electrode, and a liquid crystal layer. The reflective electrodes are provided for each of the pixels, and each of them includes a plurality of electrodes, with a combination of the areas of which area coverage modulation is performed by using n bits. The electrodes are configured such that a ratio of the sum of the perimeter(s) of electrode(s) corresponding to each bit of the n bits satisfies 1:2: . . . :2 n−1 . The liquid crystal layer is provided between the reflective electrode and the counter electrode. The semi-transmissive liquid crystal display device is configured to carry out reflective display using the reflective electrode and carry out transmissive display using at least a space of the reflective electrode between the pixels.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application is a continuation application of U.S.application Ser. No. 13/943,203, filed Jul. 16, 2013, which applicationclaims priority to Japanese Patent Application JP 2012-159877 filed inthe Japan Patent Office on Jul. 18, 2012, the entire content of which ishereby incorporated by reference.

BACKGROUND

1. Technical Field

The present disclosure relates to a semi-transmissive liquid crystaldisplay device and an electronic apparatus.

2. Description of the Related Art

Types of display devices include transmissive display devices andreflective display devices. Transmissive display devices carry outdisplay using transmitted light of backlight output from the backsurface of a screen. Reflective display devices carry out display usingreflected light of outer light. Transmissive display devices providehigh saturation and provide a screen easy to see in dark environment.Reflective display devices require less power consumption and provide ascreen easy to see in bright environment.

Furthermore, types of display devices include semi-transmissive liquidcrystal display devices that have the characteristics of transmissivedisplay devices and reflective display devices. Japanese PatentApplication Laid-open Publication No. 2009-93115, for example, disclosesa semi-transmissive liquid crystal display device including atransmissive display area (a transmissive display portion) and areflective display area (a reflective display portion) in a pixel.Semi-transmissive liquid crystal display devices carry out display usingtransmitted light of backlight in dark environment and carry out displayusing reflected light of outer light in bright environment.

Semi-transmissive liquid crystal display devices provide a screen easyto see both in the bright environment and the dark environment andrequire less power consumption. For these reasons, semi-transmissiveliquid crystal display devices are used as a display unit of electronicapparatuses, specifically, of mobile electronic apparatuses (mobiledevices) frequently used outdoors including mobile information devices,such as digital cameras, and mobile communication devices, such asmobile

Such semi-transmissive liquid crystal display devices have a trade-offbetween securement of a transmissive display area and maintenance ofreflective display performance. In other words, significant securementof the transmissive display area for improvement in transmissive displayperformance requires reduction in the reflective display areacorresponding thereto, thereby reducing the reflective displayperformance. By contrast, maintenance of reflective display performanceequivalent to that of a reflective display device requires significantsecurement of the reflective display area, thereby reducing thetransmissive display performance corresponding thereto.

For the foregoing reasons, there is a need for a semi-transmissiveliquid crystal display device that can carry out transmissive displaywhile maintaining reflective display performance equivalent to that of areflective display device and an electronic apparatus including thesemi-transmissive liquid crystal display device.

SUMMARY

According to an aspect, a semi-transmissive liquid crystal displaydevice includes a plurality of pixels arranged in a matrix, a pluralityof reflective electrodes, a counter electrode facing the reflectiveelectrode, and a liquid crystal layer. The reflective electrodes areprovided for each of the pixels, and each of them includes a pluralityof electrodes, with a combination of the areas of which area coveragemodulation is performed by using n bits, where n is an integer equal toor more than 2. The electrodes are configured such that a ratio of thesum of the perimeter(s) of electrode(s) corresponding to each bit of then bits satisfies 1:2: . . . :2^(n−1). The liquid crystal layer isprovided between the reflective electrode and the counter electrode. Thesemi-transmissive liquid crystal display device is configured to carryout reflective display using the reflective electrode and carry outtransmissive display using at least a space of the reflective electrodesbetween the pixels.

According to another aspect, a semi-transmissive liquid crystal displaydevice includes a plurality of pixels arranged in a matrix, a pluralityof reflective electrodes, a counter electrode facing the reflectiveelectrode, and a liquid crystal layer. The reflective electrodes areprovided for each of the pixels, and each of them includes a pluralityof electrodes, with a combination of the areas of which area coveragemodulation is performed by using n bits, where n is an integer equal toor more than 2. The electrodes are configured such that a ratio of thesum of the perimeter(s) of electrode(s) corresponding to each bit of then bits satisfies 1:2: . . . :2^(n−1) in an opening of the pixel. Theliquid crystal layer is provided between the reflective electrode andthe counter electrode. The semi-transmissive liquid crystal displaydevice is configured to carry out reflective display using thereflective electrode and carry out transmissive display using at least aspace of the reflective electrodes between the pixels.

According to another aspect, an electronic apparatus includes asemi-transmissive liquid crystal display device. The semi-transmissiveliquid crystal display device includes a plurality of pixels arranged ina matrix, a plurality of reflective electrodes, a counter electrodefacing the reflective electrode, and a liquid crystal layer. Thereflective electrodes are provided for each of the pixels, and each ofthem includes a plurality of electrodes, with a combination of the areasof which area coverage modulation is performed by using n bits, where nis an integer equal to or more than 2. The electrodes are configuredsuch that a ratio of the sum of the perimeter(s) of electrode(s)corresponding to each bit of the n bits satisfies 1:2: . . . :2^(n−1).The liquid crystal layer is provided between the reflective electrodeand the counter electrode. The semi-transmissive liquid crystal displaydevice is configured to carry out reflective display using thereflective electrode and carry out transmissive display using at least aspace of the reflective electrodes between the pixels.

Additional features and advantages are described herein, and will beapparent from the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a perspective view schematically illustrating a configurationof a semi-transmissive liquid crystal display device, to which thepresent disclosure can be applied, with a part thereof cut out;

FIG. 2A is a circuit diagram of a basic pixel circuit;

FIG. 2B is a schematic diagram of a pixel in color display device;

FIG. 2C a schematic diagram of pixels in monochrome display device;

FIG. 3A is a plan view of a pixel unit of a reflective liquid crystaldisplay device;

FIG. 3B is a plan view of a pixel unit of a semi-transmissive liquidcrystal display device;

FIG. 4 is a plan view of an electrode structure of a pixel unitaccording to an embodiment;

FIG. 5A is a diagram of a simulation result for explaining a reason whya frame-inversion driving method is preferably employed when no voltageis applied;

FIG. 5B is a diagram of a simulation result for explaining a reason whythe frame-inversion driving method is preferably employed when a voltageis applied in line inversion or dot inversion;

FIG. 5C is a diagram of a simulation result for explaining a reason whythe frame-inversion driving method is preferably employed when a voltageis applied upon frame inversion;

FIG. 6 is a block diagram of an exemplary circuit configuration of apixel that employs an MIP system;

FIG. 7 is a timing chart for explaining an operation of the pixel thatemploys the MIP system;

FIG. 8A is a view for explaining pixel division in an area coveragemodulation method;

FIG. 8B is another view for explaining pixel division in the areacoverage modulation method;

FIG. 8C is still another view for explaining pixel division in the areacoverage modulation method;

FIG. 8D is still another view for explaining pixel division in the areacoverage modulation method;

FIG. 8E is still another view for explaining pixel division in the areacoverage modulation method;

FIG. 8F is still another view for explaining pixel division in the areacoverage modulation method;

FIG. 9A is a view of pixels for constituting a color image, viewed fromthe color-filter side;

FIG. 9B is another view of pixels for constituting a color image, viewedfrom the color-filter side;

FIG. 10A is a view illustrating gradation=0 in 2-bit area coveragemodulation using the semi-transmissive liquid crystal display deviceaccording to the embodiment;

FIG. 10B is a view illustrating gradation=1 in 2-bit area coveragemodulation using the semi-transmissive liquid crystal display deviceaccording to the embodiment;

FIG. 10C is a view illustrating gradation=2 in 2-bit area coveragemodulation using the semi-transmissive liquid crystal display deviceaccording to the embodiment;

FIG. 10D is a view illustrating gradation=3 in 2-bit area coveragemodulation using the semi-transmissive liquid crystal display deviceaccording to the embodiment;

FIG. 11A is a diagram illustrating a relation between the luminance andthe gradation in display of white (W);

FIG. 11B is a diagram illustrating a relation between the luminance andthe gradation in display of green (G);

FIG. 11C is a diagram illustrating a relation between the luminance andthe gradation in display of red (R);

FIG. 11D is a diagram illustrating a relation between the luminance andthe gradation in display of blue (B);

FIG. 12 is a view illustrating a gap between adjacent reflectiveelectrodes;

FIG. 13 is a view illustrating movement of liquid crystal moleculesbetween pixels in transmissive display using a space of reflectiveelectrodes between the pixels;

FIG. 14 is a diagram illustrating a simulation result of transmittancebetween pixels in a normally white mode;

FIG. 15A is a view of color pixels divided with a black matrix;

FIG. 15B is another view of the color pixels divided with the blackmatrix;

FIG. 15C is a view of color pixels divided with an overlapping portionof color filters;

FIG. 15D is another view of the color pixels divided with theoverlapping portion of the color filters;

FIG. 16 is a sectional view of an example of a semi-transmissive liquidcrystal display device having a scattering layer that scatters light;

FIG. 17 is a sectional view of the scattering layer;

FIG. 18 is a plan view of an example of the scattering layer;

FIG. 19 is a plan view of another example of the scattering layer;

FIG. 20 is a sectional view of a sectional structure of two pixelsadjacent to each other in a row direction of a semi-transmissive liquidcrystal display device having a single-gap structure;

FIG. 21A is a diagram illustrating an example of optical design of anormally black ECB mode in the single-gap structure;

FIG. 21B is another diagram illustrating the example of optical designof the normally black ECB mode in the single-gap structure;

FIG. 22 is a sectional view of a sectional structure of two pixelsadjacent to each other in a row direction of a semi-transmissive liquidcrystal display device having a multi-gap structure;

FIG. 23 is a diagram illustrating a calculation result of a spectrum ina reflective display area;

FIG. 24 is a diagram illustrating a calculation result of a spectrum ina transmissive display area;

FIG. 25 is a plan view of an electrode structure of a pixel unitaccording to a modification;

FIG. 26A is a perspective view of an appearance of a digital camera towhich the present disclosure can be applied;

FIG. 26B is another perspective view of the appearance of the digitalcamera to which the present disclosure can be applied;

FIG. 27 is a perspective view of an appearance of a video camera towhich the present disclosure can be applied;

FIG. 28 is a perspective view of an appearance of a portable personalcomputer to which the present disclosure can be applied;

FIG. 29A is a front view of a mobile phone to which the presentdisclosure can be applied in an unfolded state;

FIG. 29B is a side view of the mobile phone to which the presentdisclosure can be applied;

FIG. 29C is a front view of the mobile phone to which the presentdisclosure is applied can be a folded state;

FIG. 29D is a left side view of the mobile phone to which the presentdisclosure can be applied;

FIG. 29E is a right side view of the mobile phone to which the presentdisclosure can be applied;

FIG. 29F is a top view of the mobile phone to which the presentdisclosure can be applied; and

FIG. 29G is a bottom view of the mobile phone to which the presentdisclosure can be applied.

DETAILED DESCRIPTION

Examples for embodying technologies according to the present disclosure(hereinafter, referred to as “embodiments”) are described below ingreater detail with reference to the accompanying drawings in thefollowing order:

1. Semi-transmissive liquid crystal display device to which the presentdisclosure can be applied

-   -   1-1. Semi-transmissive liquid crystal display device supporting        color display    -   1-2. Basic pixel circuit    -   1-3. Pixel and sub-pixel    -   1-4. Study of electrode structure of pixel unit

2. Description of embodiments

-   -   2-1. Method for driving liquid crystal display panel    -   2-2. MIP system    -   2-3. Area coverage modulation method    -   2-4. Display mode    -   2-5. Specific example

3. Modifications

4. Electronic apparatuses

1. SEMI-TRANSMISSIVE LIQUID CRYSTAL DISPLAY DEVICE TO WHICH THE PRESENTDISCLOSURE CAN BE APPLIED

The technologies according to the present disclosure are applicable to aflat-panel (flat) display device. Examples of the flat-panel displaydevice may include display devices provided with a liquid crystaldisplay (LCD) panel, display devices provided with anelectroluminescence (EL) display panel, and display devices providedwith a plasma display (PD) panel.

These flat-panel display devices can be classified by their displaytypes into transmissive display devices, reflective display devices, andsemi-transmissive display devices. The technologies according to thepresent disclosure are applicable to semi-transmissive liquid crystaldisplay device that have the characteristics of transmissive displaydevices and reflective display devices. In other words, thesemi-transmissive liquid crystal display devices provide a screen easyto see both under the bright environment and the dark environment andrequires less power consumption. The semi-transmissive liquid crystaldisplay device having these characteristics is preferably used as adisplay unit of electronic apparatuses, specifically, of mobileelectronic apparatuses frequently used outdoors, that is, mobile devicesincluding mobile information devices, such as digital cameras, andmobile communication devices, such as mobile phones.

The semi-transmissive liquid crystal display device, to the presentdisclosure can be applied, may be a display device supporting monochromedisplay or a display device supporting color display. If thesemi-transmissive liquid crystal display device supports color display,one pixel (a unit pixel) serving as a unit that constitutes a colorimage includes a plurality of sub-pixels. More specifically, in thedisplay device supporting color display, the unit pixel includes threesub-pixels of a sub-pixel that displays red (R), a sub-pixel thatdisplays green (G), and a sub-pixel that displays blue (B), for example.

The pixel is not necessarily obtained by combining sub-pixels in thethree-primary colors of RGB. The unit pixel may be obtained by addingsub-pixels in one color or a plurality of colors to the sub-pixels inthe three primary colors of RGB. More specifically, for example, theunit pixel may be obtained by adding a sub-pixel that displays white (W)to increase the luminance or adding at least one sub-pixel that displaysa complementary color to expand a color reproduction range.

1-1. Semi-Transmissive Liquid Crystal Display Device Supporting ColorDisplay

An explanation will be made of a semi-transmissive liquid crystaldisplay device supporting color display as an example of thesemi-transmissive liquid crystal display device to which the presentdisclosure can be applied.

FIG. 1 is a perspective view schematically illustrating a configurationof the semi-transmissive liquid crystal display device supporting colordisplay, to which the present disclosure can be applied, with a partthereof cut out.

As illustrated in FIG. 1, a semi-transmissive liquid crystal displaydevice 1, to which the present disclosure can be applied, includes afirst panel unit 10, a second panel unit 20, a liquid crystal layer 30,and a backlight unit 40 as main components. The surface of the secondpanel unit 20 serves as a display surface in the semi-transmissiveliquid crystal display device 1. The first panel unit 10 and the secondpanel unit 20 are arranged in a manner facing each other with apredetermined gap interposed therebetween. Sealing the gap between thefirst panel unit 10 and the second panel unit 20 with a liquid crystalmaterial forms the liquid crystal layer 30.

The first panel unit 10 includes a polarizing plate 11, a half-waveplate 12, a quarter-wave plate 13, a first substrate 14 made of asubstrate material including transparent glass, and a planarizing film15 arranged in this order from the side opposite to the liquid crystallayer 30, that is, from the backlight unit 40 side.

The first panel unit 10 is provided with a plurality of signal lines anda plurality of scanning lines, neither of which is illustrated, formedon the first substrate 14 in a manner intersecting with each other.Sub-pixels (hereinafter, which may be simply referred to as “pixels”) 50are two-dimensionally arranged in a matrix at portions where the signallines and the scanning lines intersect with each other.

Circuit elements including switching elements and capacitative elements,such as a thin film transistor (TFT), are formed on the first substrate14 for the respective pixels 50. Formation of the planarizing film 15 onthe surface of the circuit elements, the signal lines, and the scanninglines planarizes the surface of the first panel unit 10. Reflectiveelectrodes, which will be described later, are formed on the planarizingfilm 15 for the respective pixels 50. Because the circuit elementsincluding the TFT are formed on the first substrate 14, the firstsubstrate 14 may be referred to as a TFT substrate.

The signal lines are wiring that transmits a signal (a display signal ora video signal) for driving the pixels 50. The signal lines have awiring structure extending along an arrangement direction of pixels ofpixel columns, that is, along a column direction (a Y-direction inFIG. 1) for the respective pixel columns with respect to the matrixarrangement of the pixels 50. The scanning lines are wiring thattransmits a signal (a scanning signal) for selecting the pixels 50 inunits of row. The scanning lines have a wiring structure extending alongan arrangement direction of pixels of pixel rows, that is, along a rowdirection (an X-direction in FIG. 1) for the respective pixel rows withrespect to the matrix arrangement of the pixels 50. The X-direction andthe Y-direction intersect with each other.

The second panel unit 20 includes a transparent electrode 21 formed ofan indium tin oxide (ITO) and the like, a color filter 22, a secondsubstrate 23 made of a substrate material including transparent glass, aquarter-wave plate 24, a half-wave plate 25, and a polarizing plate 26arranged in this order from the liquid crystal layer 30 side.

In the second panel unit 20, the color filter 22 has a structure inwhich filters in stripes of red (R), green (G), and blue (B) extendingin the column direction (Y-direction) are repeatedly arranged at thesame pitch as that of the pixels 50 in the row direction (X-direction),for example. Because the second substrate 23 includes the color filter(CF) 22, the second substrate 23 may be referred to as a CF substrate.

A semi-transmissive LCD panel is formed of the first panel unit 10, thesecond panel unit 20 arranged in a manner facing the first panel unit10, and the liquid crystal layer 30 arranged between the first panelunit 10 and the second panel unit 20. The top surface (surface) of thesecond panel unit 20 serves as the display surface.

The backlight unit 40 is an illuminating unit that illuminates the LCDpanel from the back side of the LCD panel, that is, from the sideopposite to the liquid crystal layer 30 of the first panel unit 10. Theconfiguration and the components of the backlight unit 40 are notparticularly restricted. The backlight unit 40 may be formed ofwell-known members including a light source, such as a light-emittingdiode (LED) and a fluorescent tube, a prism sheet, a diffusion sheet,and a light guide plate, for example.

In the semi-transmissive liquid crystal display device 1 having theconfiguration described above, the pixels 50 each include a reflectivedisplay area (a reflective display portion) and a transmissive displayarea (a transmissive display portion). As described above, thereflective display area includes the reflective electrode formed foreach of the pixels 50 on the surface of the planarizing film 15. Thereflective display area reflects, with the reflective electrode, outerlight entering from the outside through the second panel unit 20 tocarry out display with the reflected light. The transmissive displayarea transmits light output from the backlight unit 40 to carry outdisplay with the transmitted light. The transmissive display areaprovided to each of the pixels 50 will be described later in detail.

1-2. Basic Pixel Circuit

A basic pixel circuit of the pixel 50 will now be described withreference to FIG. 2A. In FIG. 2A, a direction indicated by X(X-direction) represents the row direction of the semi-transmissiveliquid crystal display device 1 illustrated in FIG. 1, and a directionindicated by Y (Y-direction) represents the column direction thereof.

As illustrated in FIG. 2A, a plurality of signal lines 61 (61 ₁, 61 ₂,61 ₃, . . . ) and a plurality of scanning lines 62 (62 ₁, 62 ₂, 62 ₃, .. . ) are arranged in a manner intersecting with each other. The pixels50 are arranged at the intersections. The scanning lines 62 (62 ₁, 62 ₂,62 ₃, . . . ) extend in the row direction (X-direction), whereas thesignal lines 61 (61 ₁, 61 ₂, 61 ₃, . . . ) extend in the columndirection (Y-direction). As described above, the signal lines 61 and thescanning lines 62 are formed on the surface of the first substrate (TFTsubstrate) 14 of the first panel unit 10. One end of each signal lines61 (61 ₁, 61 ₂, 61 ₃, . . . ) is connected to, among output terminals ofa signal output circuit 70, a terminal corresponding to the column. Oneend of each scanning lines 62 (62 ₁, 62 ₂, 62 ₃, . . . ) is connectedto, among output terminals of a scanning circuit 80, a terminalcorresponding to the row.

The pixel 50 includes a pixel transistor 51 formed of a TFT, a liquidcrystal capacitance 52, and a capacitance 53, for example. The pixeltransistor 51 includes a gate electrode connected to the scanning line62 (62 ₁, 62 ₂, 62 ₃, . . . ), and a source electrode connected to thesignal line 61 (61 ₁, 61 ₂, 61 ₃, . . . ).

The liquid crystal capacitance 52 is a capacitance component of theliquid crystal material generated between a pixel electrode and acounter electrode (corresponding to the transparent electrode 21 inFIG. 1) formed in a manner facing the pixel electrode. The pixelelectrode is connected to a drain electrode of the pixel transistor 51.The pixel electrode corresponds to a reflective electrode formed foreach sub-pixel in color display and to a reflective electrode formed foreach pixel in monochrome display. A common electric potential V_(COM) ofa direct-current (DC) voltage is commonly applied to the counterelectrodes of the liquid crystal capacitances 52 in all the pixels. Thecapacitance 53 includes one electrode connected to the pixel electrodeof the liquid crystal capacitance 52, and the other electrode connectedto the counter electrode of the liquid crystal capacitance 52.

As is clear from the pixel circuit described above, the signal lines 61(61 ₁, 61 ₂, 61 ₃, . . . ) are wiring that transmits a signal fordriving the pixels 50, that is, a video signal output from the signaloutput circuit 70 to the pixels 50 in each pixel column. The scanninglines 62 (62 ₁, 62 ₂, 62 ₃, . . . ) are wiring that transmits a signalfor selecting the pixels 50 in units of row, that is, a scanning signaloutput from the scanning circuit 80 to each pixel row.

1-3. Pixel and Sub-Pixel

If the semi-transmissive liquid crystal display device 1 supports colordisplay, one pixel serving as a unit that constitutes a color image,that is, a unit pixel 5 includes a plurality of sub-pixels 50, forexample, as illustrated in FIG. 2B. In this example, the unit pixel 5includes a sub-pixel 50R that displays R, a sub-pixel 50B that displaysB, and a sub-pixel 50G that displays G. The sub-pixels 50R, 50B, and 50Gincluded in the unit pixel 5 are arranged in the X-direction, that is,in the row direction of the semi-transmissive liquid crystal displaydevice 1. The unit pixel 5 may further include sub-pixels in one coloror a plurality of colors as described above. If the semi-transmissiveliquid crystal display device 1 supports monochrome display alone, onepixel serving as a unit that constitutes a monochrome image, that is, aunit pixel 5M is the pixel 50 (corresponding to the sub-pixel 50 incolor display) as illustrated in FIG. 2C. The unit pixel 5 is a basicunit that displays a color image, whereas the unit pixel 5M is a basicunit that displays a monochrome image.

1-4. Study of Electrode Structure of Pixel Unit

Before the explanation of the transmissive display area, the electrodestructure of the pixel 50 will be studied.

FIGS. 3A and 3B are views for explaining an electrode structure of apixel unit of the related art. FIG. 3A is a plan view of a pixel unit ofa reflective (total reflective) liquid crystal display device. FIG. 3Bis a plan view of a pixel unit of a semi-transmissive liquid crystaldisplay device. In FIG. 3A and FIG. 3B, a reflective electrode 63 isindicated by shading.

As illustrated in FIG. 3A and FIG. 3B, a pixel unit of a liquid crystaldisplay device typically has the following structure: the pixels 50 arearranged in a matrix; the signal lines 61 are arranged at spatialpositions between the pixels 50 extending along the column directionwith respect to the matrix array; and the scanning lines 62 are arrangedat spatial positions between the pixels 50 extending along the rowdirection. As described above, the signal lines 61 and the scanninglines 62 are arranged in a manner intersecting with each other on thefirst substrate 14 of the first panel unit 10 in FIG. 1.

In the pixel unit (pixel array unit) having such a structure, thereflective liquid crystal display device illustrated in FIG. 3A has thereflective electrode 63 made of a metal, such as aluminum, in a sizenearly the same as that of the pixel 50. The reflective liquid crystaldisplay device uses the area of the reflective electrode 63 as thereflective display area. In other words, the reflective liquid crystaldisplay device secures the reflective display area in a size nearly thesame as that of the pixel 50, thereby providing desired reflectivedisplay performance.

By contrast, the semi-transmissive liquid crystal display deviceillustrated in FIG. 3B has the reflective electrode 63 and an opening 64in one pixel 50 and uses the opening 64 as the transmissive displayarea. Forming the opening 64 in the pixel 50 for securement of thetransmissive display area cannot avoid reduction in the reflectiveelectrode 63, that is, in the reflective display area corresponding tothe area of the opening 64. As a result, the semi-transmissive liquidcrystal display device may provide reflective display performance lowerthan that of the reflective liquid crystal display device. In otherwords, securement of the transmissive display area and maintenance ofthe reflective display performance are in a trade-off relation.

2. DESCRIPTION OF EMBODIMENTS

To carry out transmissive display while maintaining reflective displayperformance equivalent to that of a reflective display device, thesemi-transmissive liquid crystal display device 1 according to anembodiment of the present disclosure carries out transmissive displayusing a space of the reflective electrodes 63 between the pixels 50.Specifically, as illustrated in FIG. 4, the signal lines 61, thescanning lines 62, and other lines are arranged so as not to block thespace of the reflective electrodes 63 between the pixels 50 in the pixelunit formed of the pixels 50 arranged in a matrix. Thus, thesemi-transmissive liquid crystal display device 1 can carry outtransmissive display using the space as the transmissive display area.

The reflective electrode 63 is indicated by shading in FIG. 4. Thespaces of the reflective electrodes 63 between the pixels 50 include aspace 65 _(A) and a space 65 _(B). The space 65 _(A) extends along thearrangement direction of the pixels in the pixel columns, that is, alongthe column direction (Y-direction in FIG. 4). The space 65 _(B) extendsalong the arrangement direction of the pixels in the pixel rows, thatis, along the row direction (X-direction in FIG. 4). While the signallines 61 and the scanning lines 62 are described as an example of thewiring formed in the pixel unit in the present embodiment, the wiringformed in the pixel unit is not limited thereto. In other words, all thedrive lines (control lines) required for driving (controlling) thepixels 50 are included in the wiring in the present embodiment.

“Not blocking the space” does not mean absence of an area in which thewiring overlaps with the space 65 _(A) or 65 _(B) of the reflectiveelectrodes 63 between the pixels 50. Specifically, the concept of “notblocking the space” includes: a state where the signal lines 61 arrangedin the column direction overlap with the spaces 65 _(B) extending in therow direction; and a state where the scanning lines 62 arranged in therow direction overlap with the spaces 65 _(A) extending in the columndirection.

Furthermore, the concept of “not blocking the space” also includes: astate where the signal lines 61 partially or in a part thereof overlapwith the spaces 65 _(A) extending in the column direction; and a statewhere the scanning lines 62 partially or in a part thereof overlap withthe spaces 65 _(B) extending in the row direction. In both the cases,areas in which the signal line 61 and the scanning line 62 overlap withneither of the spaces 65 _(A) and 65 _(B) are used as the transmissivedisplay area.

To form the wiring so as not to block the spaces 65 _(A) and 65 _(B) ofthe reflective electrodes 63 between the pixels 50, the wiring ispreferably formed in a manner avoiding at least either one of the spaces65 _(A) and 65 _(B) of the reflective electrodes 63 between the pixels50. “Avoiding the spaces” means a state where the wiring is not presentin the space 65 _(A) or 65 _(B) of the reflective electrodes 63 betweenthe pixels 50 (that is, at least either one of the spaces 65 _(A) and 65_(B) has no area in which the wiring overlaps therewith).

Specifically, as illustrated in FIG. 4, the signal lines 61 arepreferably arranged in a manner avoiding the spaces 65 _(A) extending inthe column direction, that is, in a manner forming no area (portion)thereof overlapping with the spaces 65 _(A). The scanning lines 62 arepreferably arranged in a manner avoiding the spaces 65 _(B) extending inthe row direction, that is, in a manner forming no area thereofoverlapping with the spaces 65 _(B). The spaces 65 _(A) and 65 _(B) ofthe reflective electrodes 63 between the pixels 50 have no area in whichthe signal lines 61 and the scanning lines 62 overlap therewith,respectively. This makes it possible to use the essentially whole areaof the spaces 65 _(A) and 65 _(B) as the transmissive display area. As aresult, the semi-transmissive liquid crystal display device 1 canprovide higher transmissive display performance.

As described above, the semi-transmissive liquid crystal display device1 carries out transmissive display using the space of the reflectiveelectrodes 63 between the pixels 50, that is, using the area of thespace as the transmissive display area. Thus, it is not necessary tosecure the transmissive display area separately in the pixel 50. Thus,as is clear from the comparison between FIG. 3A and FIG. 4, thesemi-transmissive liquid crystal display device 1 can make the size ofthe reflective electrode 63 equivalent to that of the reflective liquidcrystal display device, if the pixels 50 are formed in the same size. Asa result, the semi-transmissive liquid crystal display device 1 cancarry out transmissive display while maintaining reflective displayperformance equivalent to that of the reflective display device.

2-1. Method for Driving Liquid Crystal Display Panel

To suppress deterioration of the resistivity (substance-specificresistance) and the like of the liquid crystal caused by continuing toapply a DC voltage having the same polarity to the liquid crystal, theLCD panel (liquid crystal display device) employs a driving method forreversing the polarity of a video signal with respect to the commonelectric potential V_(COM) at a predetermined period.

Some types of methods for driving the LCD panel are known, includingline inversion, dot inversion, and frame inversion. The line inversionis a driving method for reversing the polarity of a video signal at atime period of 1H (H represents a horizontal period) corresponding toone line (one pixel row). The dot inversion is a driving method foralternately reversing the polarity of a video signal for pixelsvertically and horizontally adjacent to each other. The frame inversionis a driving method for reversing the polarity of a video signal to bewritten to all the pixels in one frame corresponding to one screen withthe same polarity at a time.

The semi-transmissive liquid crystal display device 1 according to thepresent embodiment can employ any one of the driving methods describedabove. The semi-transmissive liquid crystal display device 1 preferablyemploys the frame-inversion driving method rather than theline-inversion or dot-inversion driving method for the reasons describedbelow.

The reason why the semi-transmissive liquid crystal display device 1preferably employs the frame-inversion driving method will be describedwith reference to simulation results of FIGS. 5A to 5C. In FIGS. 5A to5C, FIG. 5A illustrates a simulation result obtained when no voltage isapplied to the pixels 50. FIG. 5B illustrates a simulation resultobtained when a voltage is applied to the pixels 50 in the lineinversion or the dot inversion. FIG. 5C illustrates a simulation resultobtained when a voltage is applied to the pixels 50 in the frameinversion. In FIG. 5B and FIG. 5C, equipotential lines are representedby dashed-dotted lines.

In the line inversion or the dot inversion, the electric potentialbetween the transparent electrode (counter electrode) 21 and thereflective electrode (pixel electrode) 63 varies between two adjacentpixels. As a result, behavior of liquid crystal molecules between thepixels varies between near one pixel and the other pixel, therebyrendering liquid crystal orientation between the pixels unstable. Thisis quite evident from distribution of the equipotential linesrepresented by the dashed-dotted lines in FIG. 5B.

As described above, the line inversion or the dot inversion with theelectric potential varying between two adjacent pixels cannot controlthe liquid crystal orientation between the pixels stably. Transmissivedisplay using the space between the pixels, in which the liquid crystalorientation is unstable, as the transmissive display area may possiblygenerate a residual image, for example.

By contrast, in the frame inversion, the electric potential between thetransparent electrode 21 and the reflective electrode 63 is the same attwo adjacent pixels. As a result, the liquid crystal molecules betweenthe pixels behave in a similar manner near one pixel and the otherpixel. Thus, the liquid crystal orientation between the pixels is morestable in the frame-inversion driving method than in the line inversionor the dot inversion. This is quite evident from distribution of theequipotential lines represented by the dashed-dotted lines in FIG. 5C.

As described above, the frame inversion having the same electricpotential between two adjacent pixels can control the liquid crystalorientation between the pixels relatively stably. As a result,transmissive display using the space between the pixels as thetransmissive display area can suppress generation of a residual imageeffectively. For the reasons described above, the frame-inversiondriving method is preferably used rather than the line-inversion ordot-inversion driving method to carry out transmissive display using thespace of the reflective electrodes 63 between the pixels 50. Asdescribed above, it is not intended to exclude employment of theline-inversion or dot-inversion driving method.

2-2. MIP System

Because the frame-inversion driving method applies a signal voltagehaving the same polarity to the signal lines during one frame period,shading may possibly occur. To address this, the semi-transmissiveliquid crystal display device 1 employs what is called a memory in pixel(MIP) system in the frame-inversion driving method. The MIP system usesa pixel having a memory function, that is, a pixel having a memorycapable of storing therein data as the pixel 50, for example. The MIPsystem constantly applies a steady voltage to the pixel 50, therebyreducing the shading.

The MIP system includes a memory that stores therein data in a pixel,thereby carrying out display in an analog display mode and display in amemory display mode. The analog display mode is a display mode fordisplaying the gradation of a pixel in an analog manner. The memorydisplay mode is a display mode for displaying the gradation of a pixelin a digital manner based on binary information (logic “1”/logic “0”)stored in the memory in the pixel.

Because the memory display mode uses the information stored in thememory, it is not necessary to perform a writing operation of a signalelectric potential reflecting the gradation with a frame cycle. Thus,the memory display mode requires lower power consumption than the analogdisplay mode that needs to perform the writing operation of the signalelectric potential reflecting the gradation at the frame period. Inother words, the memory display mode can reduce the power consumption ofthe semi-transmissive liquid crystal display device 1.

FIG. 6 is a block diagram of an exemplary circuit configuration of apixel that employs the MIP system. In FIG. 6, components similar tothose in FIG. 2A are denoted by the same reference numerals. FIG. 7 is atiming chart for explaining an operation of the pixel that employs theMIP system.

As illustrated in FIG. 6, the pixel 50 includes a drive circuit unit 58provided with three switching elements 54 to 56 and a latch 57 inaddition to the liquid crystal capacitance (liquid crystal cell) 52. Thedrive circuit unit 58 has a static random access memory (SRAM) function.The pixel 50 including the drive circuit unit 58 has a pixelconfiguration with the SRAM function. The liquid crystal capacitance(liquid crystal cell) 52 is a liquid crystal capacitance generatedbetween a pixel electrode (e.g., the reflective electrode 63 in FIG. 4)and a counter electrode arranged in a manner facing the pixel electrode.

One end of the switching element 54 is connected to the signal line 61(corresponding to the signal lines 61 ₁ to 61 ₃ in FIG. 2A). Receiving ascanning signal φV from the scanning circuit 80 illustrated in FIG. 2Abrings the switching element 54 into an ON (closed) state. Thus, theswitching element 54 retrieves data SIG supplied from the signal outputcircuit 70 illustrated in FIG. 2A via the signal line 61. The latch 57includes inverters 571 and 572 connected in parallel and opposite toeach other. The latch 57 retains (latches) the electric potentialcorresponding to the data SIG retrieved by the switching element 54.

First ends of the switching elements 55 and 56 are supplied with acontrol pulse XFRP in the reversed phase of the common electricpotential V_(COM) and a control pulse FRP in phase thereof,respectively. Second ends of the switching elements 55 and 56 arecommonly connected, and the common connection node serves as an outputnode N_(out) in the pixel circuit. One of the switching elements 55 and56 is brought into an ON-state correspondingly to the polarity of theholding potential in the latch 57. Thus, the control pulse FRP or thecontrol pulse XFRP is applied to the pixel electrode (e.g., thereflective electrode 63 in FIG. 4) of the liquid crystal capacitance 52in which the common electric potential V_(COM) is applied to the counterelectrode (e.g., the transparent electrode 21 in FIG. 1).

As is clear from FIG. 7, if the polarity of the holding potential in thelatch 57 is negative, the pixel potential of the liquid crystalcapacitance 52 is in phase of the common electric potential V_(COM),resulting in black display in the present embodiment. If the polarity ofthe holding potential in the latch 57 is positive, the pixel potentialof the liquid crystal capacitance 52 is in the reversed phase of thecommon electric potential V_(COM), resulting in white display.

As described above, the pixel 50 in the MIP system brings one of theswitching elements 55 and 56 into an ON state in accordance with thepolarity of the holding potential in the latch 57. Thus, the controlpulse FRP or the control pulse XFRP is applied to the pixel electrode(e.g., the reflective electrode 63 in FIG. 4) of the liquid crystalcapacitance 52. As a result, a steady voltage is constantly applied tothe pixel 50, thereby suppressing occurrence of shading.

While the explanation has been made of the case where the pixel 50 isprovided with an SRAM as the internal memory in the present embodiment,the SRAM is given just as an example. The pixel 50 may be provided withanother memory, such as a dynamic random access memory (DRAM), forexample.

2-3. Area Coverage Modulation Method

The MIP system can represent only 2 gradations by using 1 bit for eachpixel 50. To employ the MIP system in the semi-transmissive liquidcrystal display device 1, an area coverage modulation method ispreferably used. The area coverage modulation method is a gradationrepresentation method for representing 4 gradations by using 2 bits byweighting a pixel area (an area of the pixel electrode) with 2:1, forexample. The area coverage modulation method will be described later indetail.

Specifically, the semi-transmissive liquid crystal display device 1employs an area coverage modulation method for dividing the reflectiveelectrode 63 (refer to FIG. 4) serving as the reflective display area ofthe pixel 50 into a plurality of electrodes weighted by the area. Thesemi-transmissive liquid crystal display device 1 transmits the pixelpotential selected based on the holding potential in the latch 57 to thedivided pixel electrodes weighted by the area. Thus, thesemi-transmissive liquid crystal display device 1 displays thegradations with a combination of the areas thus weighted. Hereinafter,the electrodes obtained by dividing the reflective electrode 63 in amanner weighted by the area may be referred to as the divided pixelelectrodes.

The area coverage modulation method will now be specifically described.The area coverage modulation method is a gradation representation methodfor representing 2×N gradations with N electrodes obtained by weightingan area ratio with 2⁰, 2¹, 2², . . . , 2^(N−1), for example (in the casewhere each bit for displaying the gradation corresponds to one ofelectrodes). In the case where each bit for displaying the gradation maycorrespond to a plurality of electrodes, the area coverage modulationmethod weights the area ratio of the electrodes corresponding torespective bits with 2⁰, 2¹, 2², . . . , 2^(N−1), for example, therebydisplaying 2^(N) gradations by using N bits.

The area coverage modulation method is employed to reduce non-uniformityof image quality caused by fluctuation in TFT characteristics, forexample. The semi-transmissive liquid crystal display device 1 employs a2-bit area coverage modulation method for representing 4 gradations withthe area (pixel area) of the reflective electrode 63 serving as thepixel electrode divided with the weight of 2:1.

To weight the pixel area with 2:1, the pixel electrode of the pixel 50is typically divided into a divided pixel electrode 501 with an area Sand a divided pixel electrode 502 with an area twice as large as that ofthe divided pixel electrode 501 (an area 2×S) like a reflectiveelectrode 63A illustrated in FIG. 8A. The structure of the reflectiveelectrode 63A, however, is not preferably used in terms of gradationrepresentation because the centers of gravity of respective gradationsare not aligned with (do not coincide with) the center of gravity of onepixel of the pixel 50.

To align the centers of gravity of the respective gradations with thecenter of gravity of one pixel of the pixel 50, the following structuremay be employed: a rectangular area is cut out from the center of adivided pixel electrode 504 with an area 2×S; and a divided pixelelectrode 503 with an area S is arranged at the center of therectangular area thus cut-out like a reflective electrode 63Billustrated in FIG. 8B. In the structure of the reflective electrode63B, however, connections 504A and 504B of the divided pixel electrode504 positioned on both sides of the divided pixel electrode 503 have asmall width. This reduces the reflective area of the whole divided pixelelectrode 504 and makes it difficult to align the liquid crystal aroundthe connections 504A and 504B.

As described above, when a vertical aligned (VA) mode, in which liquidcrystal molecules are aligned nearly vertically with respect to thesubstrate when no electric field is formed, is adopted in area coveragemodulation, it is difficult to properly align the liquid crystal. Thisis because the action of the voltage on the liquid crystal moleculesvaries depending on the shape, the size, and other elements of theelectrode. Furthermore, because the area ratio of the reflectiveelectrodes is not necessarily equal to the reflectance ratio, it isdifficult to design the gradation. The reflectance of the reflectiveelectrode is determined by the area of the reflective electrode, theliquid crystal orientation, and other factors. In the structure of thereflective electrode 63A illustrated in FIG. 8A, an area ratio of 1:2does not make the ratio of the periphery lengths (perimeters) of theelectrodes 1:2. An assumption is made as follows: the divided pixelelectrode 501 has a square shape in a planar view, and the length of aside is L; and the divided pixel electrode 502 has a rectangular shapein a planar view, the length of a short side is L, and the length of along side is 2×L, for example. In this case, the perimeter of thedivided pixel electrode 501 is 4×L, and the perimeter of the dividedpixel electrode 502 is 6×L, thereby deriving a ratio of the perimetersof 2:3. Thus, the area ratio of the reflective electrodes is notnecessarily equal to the reflectance ratio.

To employ the area coverage modulation method in consideration of therepresentability of the gradation and effective use of the reflectivearea, a reflective electrode 63C is preferably divided into a pluralityof (three in this example) divided pixel electrodes 505, 506A, and 506Bwith the same area (size) as illustrated in FIG. 8C. The reflectiveelectrode 63C includes a plurality of (three in this example) dividedpixel electrodes 505, 506A, and 506B. A combination of these areasenables the area coverage modulation.

In the reflective electrode 63C having the electrode structure dividedinto three, the divided pixel electrodes 506A and 506B are arranged onrespective sides of the divided pixel electrode 505. In other words, thethree divided pixel electrodes 506A, 505, and 506B are arranged in linein this order. The reflective electrode 63C uses the divided pixelelectrodes 506A and 506B arranged on the respective sides of the dividedpixel electrode 505 as a pair. The reflective electrode 63C drives thepair of divided pixel electrodes 506A and 506B simultaneously, therebyweighting the pixel area with 2:1 with respect to the divided pixelelectrode 505 arranged therebetween.

To drive the two divided pixel electrodes 506A and 506B simultaneously,the two divided pixel electrodes 506A and 506B are preferably connectedto each other electrically by a conductor 510 formed of an ITO, forexample, as illustrated in FIG. 8C. Electrical connection of the twodivided pixel electrodes 506A and 506B enables the two divided pixelelectrodes 506A and 506B to be driven by a single drive circuit. As aresult, the configuration of the drive circuit unit 58 of a pixel (asub-pixel in the case of color display) can be simplified compared withthe case where the two divided pixel electrodes 506A and 506B are drivenby respective drive circuits.

The reflective electrode 63C, more specifically, a sub-pixel (a pixel inthe case of carrying out monochrome display alone) including thereflective electrode 63C can perform area coverage modulation fordisplaying 2^(n)=4 gradations by using n=2 bits (n is an integer equalto or more than 2). In this case, the sub-pixel has the respective drivecircuit unit 58 illustrated in FIG. 6 for each of the divided pixelelectrode 505 and the two divided pixel electrodes 506A and 506B. Toperform 2-bit area coverage modulation on the sub-pixel including thereflective electrode 63C, an electrode corresponding to the leastsignificant bit is the divided pixel electrode 505. An electrodecorresponding to a bit higher than the least significant bit, that is,corresponding to the most significant bit is the pair of divided pixelelectrodes 506A and 506B.

The divided pixel electrodes 506A, 505, and 506B included in thereflective electrode 63C each have a square shape in a planar view, andthe length of a side thereof is L. The divided pixel electrodes 506A,505, and 506B have the same shape and the same size. Thus, the arearatio of the divided pixel electrode 505 to the two divided pixelelectrodes 506A and 506B is 1:2. The sum of the perimeter of the dividedpixel electrode 505 is 4×L, and the sum of the perimeters of the twodivided pixel electrodes 506A and 506B is 8×L. Thus, in the reflectiveelectrode 63C capable of performing area coverage modulation by usingn=2 bits, the ratio of the sum of the perimeter of the divided pixelelectrode 505 to that of the two divided pixel electrodes 506A and 506Bcorresponding to respective bits is 1:2^(n−1)=1:2. The reflectiveelectrode 63C capable of performing area coverage modulation by using nbits (n=2 in this example) can make the area ratio of the electrodes(divided pixel electrodes 505, 506A, and 506B) corresponding torespective bits closer to the reflectance ratio. As a result, thereflective electrode 63C improves the characteristics in gradationdisplay (gradation characteristics).

As described above, the reflective electrode 63C has the two dividedpixel electrodes 506A and 506B arranged on the respective sides of thedivided pixel electrode 505. In other words, the reflective electrode63C has the two divided pixel electrodes 506A and 506B arrangedsymmetrically with respect to the divided pixel electrode 505. Thedivided pixel electrode 505 is the electrode corresponding to the leastsignificant bit in the area coverage modulation using n bits (n=2). Thetwo divided pixel electrodes 506A and 506B are the electrodescorresponding to a bit (the most significant bit in this example) higherthan the least significant bit. Thus, the reflective electrode 63C canalign the centers of gravity of respective gradations with the center ofgravity of one pixel (one sub-pixel in the case of color display),thereby improving the gradation characteristics.

A reflective electrode 63D illustrated in FIG. 8D is divided into threeto include three divided pixel electrodes 505, 506A, and 506B. Thereflective electrode 63D performs 2-bit area coverage modulation with anarea ratio of 2:1 with a combination of the areas of the two dividedpixel electrodes 506A and 506B and the divided pixel electrode 505 amongthe three divided pixel electrodes 505, 506A, and 506B. The two dividedpixel electrodes 506A and 506B are arranged adjacent to each other andare electrically connected by a conductor 511 on the same plane. Thedivided pixel electrode 506A of the two divided pixel electrodes 506Aand 506B is adjacent to the divided pixel electrode 505. The dividedpixel electrode 505 is an electrode corresponding to the leastsignificant bit. The two divided pixel electrodes 506A and 506B areelectrodes corresponding to a bit higher than the least significant bit,more specifically, corresponding to the most significant bit.

The conductor 511 is made of the same material as that of the twodivided pixel electrodes 506A and 506B. The conductor 511 is formed onthe same plane as that of the two divided pixel electrodes 506A and 506Bintegrally therewith. “The conductor 511 is formed on the same plane asthat of the two divided pixel electrodes 506A and 506B integrallytherewith” means that the conductor 511 and the two divided pixelelectrodes 506A and 506B are formed integrally on the surface of thesingle planarizing film 15 illustrated in FIG. 1.

In this example, if the three divided pixel electrodes 505, 506A, and506B have the same shape and the same size, the area and the perimeterof the conductor 511 may not be used to calculate the area ratio and theratio of the sum of the perimeters of the divided pixel electrode 505 tothe two divided pixel electrodes 506A and 506B. The area ratio of thedivided pixel electrode 505 to the two divided pixel electrodes 506A and506B is 1:2. The ratio of the sum of the perimeter of the divided pixelelectrode 505 to that of the two divided pixel electrodes 506A and 506Bcorresponding to respective bits is 1:2^(n−1)=1:2. Thus, the reflectiveelectrode 63D capable of performing area coverage modulation by using nbits (n=2 in this example) can make the area ratio of the electrodes(divided pixel electrodes 505, 506A, and 506B) corresponding torespective bits closer to the reflectance ratio.

The conductor 511 is arranged between the two divided pixel electrodes506A and 506B on the same plane to electrically connect the two dividedpixel electrodes 506A and 506B. The width (size in the X-direction inFIG. 8D) of the conductor 511 is smaller than the width (size in theX-direction in FIG. 8D) of the divided pixel electrodes 506A and 506B.In the present embodiment, the width of the conductor 511 preferablyfalls within a range of one-tenth to one-fifth of the width of thedivided pixel electrodes 506A and 506B. Formation of the conductor 511with the width falling within such a range allows the area and theperimeter of the conductor 511 to be ignored in calculation of the arearatio and the sum of the perimeters described above. In the presentembodiment, the conductor 511 is arranged at the center in the widthdirection of the two divided pixel electrodes 506A and 506B. Theposition of the conductor 511 is not limited thereto as long as theconductor 511 is arranged between the two divided pixel electrodes 506Aand 506B.

If at least one of the shapes and the sizes of the three divided pixelelectrodes 505, 506A, and 506B is different, the area and the perimeterof the conductor 511 may be used to calculate the area ratio and theratio of the sum of the perimeters of the divided pixel electrode 505 tothe two divided pixel electrodes 506A and 506B. In other words, the arearatio and the ratio of the sum of the perimeters of the divided pixelelectrode 505 to the two divided pixel electrodes 506A and 506B arecalculated including the area and the perimeter of the conductor 511(sum of the perimeter of a portion between the two divided pixelelectrodes 506A and 506B). To represent 4 gradations by using n=2 bits,the areas and the perimeters of the three divided pixel electrodes 505,506A, and 506B and the conductor 511 are adjusted such that the arearatio is 1:2 and that the ratio of the sum of the perimeters is 1:2.

To form the reflective electrode 63C illustrated in FIG. 8C, theplanarizing film 15 illustrated in FIG. 1 is formed into a two-layerstructure. The two divided pixel electrodes 506A and 506B are formed onthe surface of a second layer and connected by a conductor of an ITO andthe like formed between a first layer and the second layer. Thisimproves the gradation characteristics of the reflective electrode 63Cbut increases the manufacturing process thereof. In terms of thereflective electrode 63D illustrated in FIG. 8D, the conductor 511 andthe two divided pixel electrodes 506A and 506B are integrally formed onthe surface of the single planarizing film 15. Thus, the planarizingfilm 15 illustrated in FIG. 1 can be formed as one layer in thereflective electrode 63D, thereby keeping the number of processes fromincreasing.

Because the centers of gravity of respective gradations deviate from thecenter of gravity of one pixel (one sub-pixel in the case of colordisplay) in the reflective electrode 63D, the gradation characteristicsof the reflective electrode 63D are slightly inferior to those of thereflective electrode 63C. The gradation characteristics of thereflective electrode 63D, however, may possibly be sufficient to displaya relatively simple image alone except for the case where halftone isfrequently used like in a natural image. In this case, the use of thereflective electrode 63D for the semi-transmissive liquid crystaldisplay device 1 can reduce the manufacturing process and themanufacturing cost.

An explanation will be made of an example where 2^(n) gradations can bedisplayed by using a bit number larger than n=2. A reflective electrode63E illustrated in FIG. 8E and a reflective electrode 63F illustrated inFIG. 8F can perform area coverage modulation for displaying 2^(n)=8gradations by using n=3 bits. The reflective electrode 63E illustratedin FIG. 8E includes one divided pixel electrode 505, two divided pixelelectrodes 506A and 506B, and four divided pixel electrodes 507A, 507B,507C, and 507D. In other words, the reflective electrode 63E is obtainedby dividing one electrode into seven.

The two divided pixel electrodes 506A and 506B are electricallyconnected to each other by a conductor 510. The four divided pixelelectrodes 507A, 507B, 507C, and 507D are electrically connected to oneanother by a conductor 512. In the reflective electrode 63E, the dividedpixel electrode 505 is an electrode corresponding to the leastsignificant bit (first bit), the two divided pixel electrodes 506A and506B are electrodes corresponding to a bit (second bit) next higher thanthe least significant bit, and the four divided pixel electrodes 507A,507B, 507C, and 507D are electrodes corresponding to the mostsignificant bit (third bit). The two divided pixel electrodes 506A and506B corresponding to second bit are electrically connected to eachother. The four divided pixel electrodes 507A, 507B, 507C, and 507Dcorresponding to third bit are electrically connected to one another.Two or more electrodes (divided pixel electrodes) corresponding torespective bits are electrically connected to one another.

As illustrated in FIG. 8E, the divided pixel electrodes 506A and 506Bcorresponding to second bit are arranged on respective sides of thedivided pixel electrode 505 corresponding to first bit. The dividedpixel electrode 507A among the four divided pixel electrodes 507A, 507B,507C, and 507D corresponding to third bit is arranged adjacent to thedivided pixel electrode 506A. The divided pixel electrode 507B isarranged adjacent to the divided pixel electrode 506B. Furthermore, thedivided pixel electrode 507C is arranged adjacent to the divided pixelelectrode 507A, and the divided pixel electrode 507D is arrangedadjacent to the divided pixel electrode 507B. In the reflectiveelectrode 63E, the two divided pixel electrodes 506A and 506Bcorresponding to the bit next higher than the least significant bit arearranged on respective sides of the divided pixel electrode 505corresponding to the least significant bit. Furthermore, the fourdivided pixel electrodes 507A, 507B, 507C, and 507D corresponding to thebit higher than that of the two divided pixel electrodes 506A and 506Bare arranged two by two on respective sides of the divided pixelelectrodes 506A and 506B arranged in a manner sandwiching the dividedpixel electrode 505. In the reflective electrode 63E, the electrodescorresponding to the bits higher than the least significant bit aresymmetrically arranged with respect to the divided pixel electrode 505serving as the electrode corresponding to the least significant bit.

The reflective electrode 63F illustrated in FIG. 8F is similar to thereflective electrode 63E illustrated in FIG. 8E except for the followingpoints: the two divided pixel electrodes 507A and 507C arranged on thedivided pixel electrode 506A side among the four divided pixelelectrodes 507A, 507B, 507C, and 507D corresponding to the mostsignificant bit (third bit in this example) are electrically connectedby a conductor 514 on the same plane; the two divided pixel electrodes507B and 507D arranged on the divided pixel electrode 506B side areelectrically connected by the conductor 514 on the same plane; and thetwo divided pixel electrodes 507A and 507B among the four divided pixelelectrodes 507A, 507B, 507C, and 507D are electrically connected to eachother by a conductor 513.

Similarly to the reflective electrode 63D illustrated in FIG. 8D, if theseven divided pixel electrodes 505, 506A, 506B, 507A, 507B, 507C, and507D included in the reflective electrode 63F have the same shape andthe same size, the area and the perimeter of the conductor 514 may notbe used to calculate the area ratio and the ratio of the sum of theperimeters described above. Regarding the width (size in the X-directionin FIG. 8F) of the conductor 514 and the position at which the conductor514 is arranged, the same explanations can be given thereto with thoseof the reflective electrode 63D.

The seven divided pixel electrodes 505, 506A, 506B, 507A, 507B, 507C,and 507D included in the reflective electrodes 63E and 63F have the sameshape and the same size. The ratio (area ratio) of the area of thedivided pixel electrode 505 corresponding to first bit, the areas of thetwo divided pixel electrodes 506A and 506B corresponding to second bit,and the areas of the four divided pixel electrodes 507A, 507B, 507C, and507D corresponding to third bit is 1:2:4. The ratio of the sum of theperimeter of the divided pixel electrode 505 corresponding to first bit,the sum of the perimeters of the two divided pixel electrodes 506A and506B corresponding to second bit, and the sum of the perimeters of thefour divided pixel electrodes 507A, 507B, 507C, and 507D correspondingto third bit is 1:2:2^(n−1)=1:2:2²=1:2:4. Thus, the reflectiveelectrodes 63E and 63F capable of performing area coverage modulation byusing n bits (n=3 in this example) can make the area ratio of theelectrodes (divided pixel electrodes 505, 506A, 506B, 507A, 507B, 507C,and 507D) corresponding to respective bits closer to the reflectanceratio.

To carry out transmissive display, the reflective electrodes 63A to 63Ftransmit backlight not only through the spaces 65 _(A) and 65 _(B) ofthe reflective electrodes 63 between the pixels 50 as illustrated inFIG. 4 but also through the spaces between adjacent divided pixelelectrodes among the divided pixel electrodes 501, 502, 505, 506A, 506B,and the like. The semi-transmissive liquid crystal display device 1including one of the reflective electrodes 63A to 63F carries outtransmissive display using at least the spaces 65 _(A) and 65 _(B) ofthe reflective electrodes 63 between the pixels 50.

A pixel (color pixel) 5 a illustrated in FIG. 9A, which is configured todisplay a color image, includes sub-pixels (pixels) 50R, 50G, and 50Bcorresponding to colors of R, G, and B, respectively. The sub-pixels50R, 50G, and 50B each include a reflective electrode 63C having threedivided pixel electrodes 505, 506A, and 506B. The reflective electrode63C is the same as that illustrated in FIG. 8C. The sub-pixel 50Rcorresponding to R includes a color filter 22R, the sub-pixel 50Gcorresponding to G includes a color filter 22G, and the sub-pixel 50Bcorresponding to B includes a color filter 22B. The sub-pixels 50R, 50G,and 50B are partitioned by a black matrix BM. The areas between theblack matrixes BM are openings OP of the sub-pixels 50R, 50G, and 50B.The sub-pixels 50R, 50G, and 50B can perform area coverage modulation of4 gradations by using n=2 bits.

A pixel (color pixel) 5 b illustrated in FIG. 9B, which is configured todisplay a color image, includes sub-pixels 50Rb, 50Gb, and 50Bbcorresponding to colors of R, G, and B, respectively. The sub-pixels50Rb, 50Gb, and 50Bb each include a reflective electrode 63 b havingthree divided pixel electrodes 505 b, 506Ab, and 506Bb. The dividedpixel electrodes 506Ab, 505 b, and 506Bb are electrodes having arectangular shape in a planar view and extending in the column directionof the color pixel 5 b (Y-direction in FIG. 9B). The divided pixelelectrodes 506Ab, 505 b, and 506Bb have the same shape and the samesize.

The divided pixel electrodes 506Ab, 505 b, and 506Bb are arranged in therow direction of the color pixel 5 b (X-direction in FIG. 9B) in thisorder. The divided pixel electrodes 506Ab and 506Bb are electricallyconnected by a conductor formed of an ITO, for example. Thisconfiguration enables the sub-pixels 50Rb, 50Gb, and 50Bb to performarea coverage modulation of 4 gradations by using n=2 bits with thedivided pixel electrode 505 b and the divided pixel electrodes 506Ab and506Bb.

The sub-pixel 50Rb corresponding to R includes a color filter 22R, thesub-pixel 50Gb corresponding to G includes a color filter 22G, and thesub-pixel 50Bb corresponding to B includes a color filter 22B. Parts ofthe color filters 22R and 22G included in the sub-pixels 50Rb and 50Gb,respectively, overlap with each other. Parts of the color filters 22Gand 22B included in the sub-pixels 50Gb and 50Bb, respectively, overlapwith each other. Portions at which the color filters 22R and 22G overlapwith each other and at which the color filters 22G and 22B overlap witheach other may be referred to as an overlapping portion OL. Thesub-pixels 50Rb, 50Gb, and 50Bb are partitioned by the overlappingportion OL. The areas partitioned by the overlapping portions OL areopenings OP of the sub-pixels 50Rb, 50Gb, and 50Bb.

Because the sub-pixels 50R, 50G, and 50B are partitioned by the blackmatrix BM in the color pixel 5 a, no light passes through the spacesbetween adjacent sub-pixels among the sub-pixels 50R, 50G, and 50B inthe row direction. Because the sub-pixels 50Rb, 50Gb, and 50Bb arepartitioned by the overlapping portion OL in the color pixel 5 b, thespaces between adjacent sub-pixels among the sub-pixels 50Rb, 50Gb, and50Bb in the row direction have light lower transmittance than that ofthe spaces between adjacent sub-pixels among the sub-pixels 50Rb, 50Gb,and 50Bb in the column direction.

In the sub-pixels 50R, 50G, and 50B included in the color pixel 5 a, theratio of the sum of the perimeters in the opening OP is 1:2²⁻¹=1:2. Inother words, the sub-pixels 50R, 50G, and 50B have a ratio of the sum ofthe perimeters that are not in contact with the black matrix BM and arepresent in the openings OP of 1:2. Thus, even if the black matrix BMblocks light transmitted in the column direction, the sub-pixels 50R,50G, and 50B can make the area ratio of the electrodes (divided pixelelectrodes 505, 506A, and 506B) corresponding to respective bits closerto the reflectance ratio. The same applies to the case where no blackmatrix BM is used, the sub-pixels 50R, 50G, and 50B are partitionedusing overlapping portions between the color filters 22R and 22G andbetween 22G and 22B, and the amount of light transmitted in the columndirection is small.

By contrast, the color pixel 5 b has a small amount of transmitted lightat a portion of the divided pixel electrode 506Ab or the divided pixelelectrode 506Bb adjacent to the overlapping portion OL. For this reason,the sides of the divided pixel electrode 506Ab and the divided pixelelectrode 506Bb adjacent to the overlapping portion OL are not used tocalculate the ratio of the sum of the perimeters described above. Thus,in the sub-pixels 50Rb, 50Gb, and 50Bb included in the color pixel 5 b,the ratio of the sum of the perimeters in the opening OP is not1:2²⁻¹=1:2. The reason of this result will be specifically described.

Assuming that the length of the long side of the divided pixelelectrodes 505 b, 506Ab, and 506Bb is L, and the length of the shortside thereof is A, the perimeter of each divided pixel electrode isexpressed by 2×(L+A). In the sub-pixels 50Rb and 50Bb, the sum of theperimeter of the divided pixel electrode 505 b corresponding to theleast significant bit is 2×(L+A), and the sum of the perimeters of thedivided pixel electrodes 506Ab and 506Bb corresponding to the mostsignificant bit is 2×(L+A)+L+2×A=3×L+4×A. In the sub-pixels 50Rb and50Bb, the ratio of the sum of the perimeters of the divided pixelelectrodes 505 b, 506Ab, and 506Bb corresponding to respective bits is2×(L+A):3×L+4×A, which is not 1:2.

Similarly, in the sub-pixel 50Gb, the sum of the perimeter of thedivided pixel electrode 505 b corresponding to the least significant bitis 2×(L+A), and the sum of the perimeters of the divided pixelelectrodes 506Ab and 506Bb corresponding to the most significant bit is2×(L+2×A). In the sub-pixel 50Gb, the ratio of the sum of the perimetersof the divided pixel electrodes 505 b, 506Ab, and 506Bb corresponding torespective bits is L+A:L+2×A, which is not 1:2.

In the sub-pixels 50Rb, 50Gb, and 50Bb, the ratio of the sum of theperimeters in the opening OP is not 1:2²⁻¹=1:2. As a result, thesub-pixels 50Rb, 50Gb, and 50Bb fail to make the area ratio of theelectrodes (divided pixel electrodes 505 b, 506Ab, and 506Bb)corresponding to respective bits closer to the reflectance ratio,thereby degrading the gradation characteristics. If the sub-pixels arepartitioned by the black matrix BM or the overlapping portion OL, theratio of the sum of the perimeters that are not in contact with theblack matrix BM or the like and are present in the openings OP simplyneeds to be 1:2: . . . :2^(n−1) like the reflective electrode 63Cincluded in the sub-pixel 50R of the color pixel 5 a, for example. Thisconfiguration can make the area ratio of the electrodes (divided pixelelectrodes 505 b, 506Ab, and 506Bb) corresponding to respective bitscloser to the reflectance ratio, thereby improving the gradationcharacteristics. The relation between the gradation and the luminance ofthe semi-transmissive liquid crystal display device 1 will be described.

FIG. 10A illustrates gradation=0, FIG. 10B illustrates gradation=1, FIG.10C illustrates gradation=2, and FIG. 10D illustrates gradation=3. Inthe gradation=0, all the three divided pixel electrodes 505, 506A, and506B included in the pixel 50 display black. In the gradation=1, thedivided pixel electrode 505 displays white, and the two divided pixelelectrodes 506A and 506B display black. In the gradation=2, the twodivided pixel electrodes 506A and 506B display white, and the dividedpixel electrode 505 displays black. In the gradation=3, all the threedivided pixel electrodes 505, 506A, and 506B display white.

In the pixel 50, the luminance and the gradation may not possibly be inproportion to each other because of the shapes of the divided pixelelectrodes 505, 506A, and 506B, the way to apply the voltage, the degreeof propagation of the backlight, or the liquid crystal orientation. Thepixel 50 can perform 2-bit area coverage modulation with the dividedpixel electrode 505 and the divided pixel electrodes 506A and 506Belectrically connected to each other. The divided pixel electrode 505corresponds to the least significant bit, whereas the divided pixelelectrodes 506A and 506B correspond to the most significant bit. FIG.11A to FIG. 11D illustrate results obtained by measuring the luminanceof the pixel 50 and plotting the luminance with respect to thegradation. As illustrated in FIG. 11A to FIG. 11D, the luminance of thepixel 50 is reduced in the gradation=3 compared with in the gradation=1and gradation=2 in all the colors. This is because adjacent pixels havea great influence on each other in the gradation=3 compared with in thegradation=1 and gradation=2.

As illustrated in FIG. 10B, for example, because a voltage is appliedonly to the divided pixel electrode 505 of the pixel 50 in thegradation=1, the divided pixel electrode 505 is not affected by thedivided pixel electrodes 506A and 506B adjacent thereto. Assuming that adistance between the divided pixel electrode 505 and each of the dividedpixel electrodes 506A and 506B is d, the divided pixel electrode 505 inthe gradation=1 causes liquid crystal molecules in an area Aa beyond d/2from the divided pixel electrode 505 to move.

As illustrated in FIG. 10C, a voltage is applied to the divided pixelelectrodes 506A and 506B of the pixel 50 in the gradation=2. Because thedivided pixel electrodes 506A and 506B are arranged on respective sidesof the divided pixel electrode 505 to which no voltage is applied, thedivided pixel electrodes 506A and 506B are not affected by the dividedpixel electrode 505. Thus, the divided pixel electrodes 506A and 506B inthe gradation=2 cause liquid crystal molecules in areas Ab beyond d/2from the divided pixel electrodes 506A and 506B to move, respectively.

As illustrated in FIG. 10D, a voltage is applied to the divided pixelelectrodes 505, 506A, and 506B of the pixel 50 in the gradation=3. Thus,the divided pixel electrodes 505, 506A, and 506B are affected by oneanother at portions adjacent to one another. As a result, the dividedpixel electrodes 506A and 506B in the gradation=3 cause only liquidcrystal molecules in areas of up to d/2 from the divided pixelelectrodes 506A and 506B, that is, in areas represented by Ri of areasAc to move at the portions adjacent to the divided pixel electrode 505.The divided pixel electrode 505 in the gradation=3 cause only liquidcrystal molecules in an area of up to d/2 from the divided pixelelectrode 505, that is, in an area represented by Ri of an area Ad tomove at the portions adjacent to the divided pixel electrode 506A or506B.

In the gradation=1, the liquid crystal molecules move beyond d/2 fromthe divided pixel electrode 505 all around the divided pixel electrode505. In the gradation=2, the liquid crystal molecules move beyond d/2from the divided pixel electrodes 506A and 506B all around the dividedpixel electrodes 506A and 506B. In the gradation=3, the divided pixelelectrode 505 causes the liquid crystal molecules to move beyond d/2from the divided pixel electrode 505 at two sides thereof and move up tod/2 from the divided pixel electrode 505 at the other two sides thereof.The divided pixel electrodes 506A and 506B cause the liquid crystalmolecules to move beyond d/2 from the divided pixel electrodes 506A and506B at three sides thereof and move up to d/2 from the divided pixelelectrodes 506A and 506B at the other one side thereof, respectively.The size of the area in which the liquid crystal molecules move aroundthe divided pixel electrodes 505, 506A, and 506B increases in proportionbetween the gradation=1 and the gradation=2. By contrast, the size ofthe area in which the liquid crystal molecules move around the dividedpixel electrodes 505, 506A, and 506B does not increase in proportionbetween the gradation=2 and the gradation=3. The luminance and thegradation are not in proportion to each other in the pixel 50 becausethe size of the area in which the liquid crystal molecules move is notin proportion to the gradation.

To address this, the divided pixel electrodes 505, 506A, and 506Bserving as a plurality of electrodes included in the pixel 50 arearranged such that the luminance and the gradation change in proportionto each other in the present embodiment. Specifically, as illustrated inFIG. 12, the divided pixel electrodes 506A, 505, and 506B are arrangedsuch that a gap d between the pixels 50 adjacent to each other in thecolumn direction (Y-direction in FIG. 12) is different from a gap Dbetween the divided pixel electrodes 506A and 505 and between 505 and506B adjacent to each other in one pixel 50. In the present embodiment,d<D is satisfied. In other words, the divided pixel electrodes 506A,505, and 506B in one pixel 50 are arranged such that the divided pixelelectrode 505 corresponding to a lower bit is arranged farther away fromdivided pixel electrodes adjacent thereto than the divided pixelelectrodes 506A and 506B corresponding to a higher bit.

The divided pixel electrodes 505, 506A, and 506B are typically arrangedsuch that the gaps between adjacent electrodes among divided pixelelectrodes 505, 506A, and 506B are the same in the row direction(X-direction in FIG. 12) and the column direction. In the presentembodiment, the gaps between adjacent electrodes among divided pixelelectrodes 505, 506A, and 506B are set as follows: the gap D between thedivided pixel electrodes 506A and 505 and between 505 and 506B adjacentto each other in one pixel 50 is made larger than the gap d between thedivided pixel electrodes 506A and 506B adjacent to each other inadjacent pixels 50 in the column direction. With this configuration,application of a voltage to all the divided pixel electrodes 505, 506A,and 506B included in the pixel 50 allows the liquid crystal molecules tomove beyond one-half of the gap d between adjacent pixels 50 in theareas where the divided pixel electrode 505 is adjacent to the dividedpixel electrode 506A or 506B. This increases the luminance in thegradation=3 compared with the case where the gaps between adjacentelectrodes among divided pixel electrodes 505, 506A, and 506B are setequal to one another. As a result, the luminance and the gradationchange in proportion to each other, thereby improving the gradationcharacteristics. Furthermore, adjusting the gaps between adjacentelectrodes among divided pixel electrodes 505, 506A, and 506B, allowsthe luminance between the gradations to be adjusted in a relativelysimple manner.

As described above, the reflective electrodes 63C to 63F included in thesemi-transmissive liquid crystal display device 1 include the dividedpixel electrodes 505, 506A, 506B, and the like serving as a plurality ofelectrodes provided to each of the pixels (sub-pixels in color display)50 in the present embodiment. The reflective electrodes 63C to 63F canperform area coverage modulation for displaying 2^(n) gradations byusing n bits with a combination of the areas of the divided pixelelectrodes. The ratio of the sum of the perimeters of the divided pixelelectrodes 505, 506A, 506B, and the like corresponding to respectivebits is 1:2: . . . :2^(n−1). Thus, the reflective electrodes 63C to 63Fcapable of performing area coverage modulation by using n bits can makethe area ratio of the electrodes (divided pixel electrodes 505, 506A,506B, and the like) corresponding to respective bits closer to thereflectance ratio, thereby improving the gradation characteristics.Furthermore, the structures of the divided pixel electrodes 505, 506A,506B, and the like having the same size and the same shape relativelyfacilitate designing and manufacturing the divided pixel electrodes 505,506A, 506B, and the like. The explanation has been made of the casewhere the shape of the divided pixel electrodes 505, 506A, 506B and thelike is a square or a rectangle. However, the shape of the divided pixelelectrodes 505, 506A, 506B, and the like is not limited to a square or arectangle as long as the area ratio and the ratio of the sum of theperimeters fall within the range in the present embodiment.

While the explanation has been made of the case where the area coveragemodulation method is used to employ the MIP system in the presentembodiment, other gradation methods, such as a time-division gradationmethod, may be used. In the time-division gradation method, however, thepixel potential changes depending on time even in a still image, therebycausing liquid crystal molecules in a pixel and between pixels to move.For this reason, the area coverage modulation method is more preferablyused than the time-division gradation method. Furthermore, the areacoverage modulation method divides the pixel electrode, that is, thereflective electrode 63, thereby increasing the gap between theelectrodes. This advantageously increases the transmittance of the panelcompared with the case where the reflective electrode 63 is not divided.

While the explanation has been made of the case where a pixel of MIPhaving a memory capable of storing therein data is used as a pixelhaving a memory function, it is given just as an example. Examples ofthe pixel having a memory function may include a pixel provided with awell-known memory liquid crystal as well as the pixel of MIP.

2-4. Display Mode

Display modes of liquid crystal include a normally white mode and anormally black mode. In the normally white mode, application of noelectric field (voltage) causes the liquid crystal to display white, andapplication of an electric filed causes the liquid crystal to displayblack. In the normally black mode, application of no electric fieldcauses the liquid crystal to display black, and application of anelectric filed causes the liquid crystal to display white. The modes arethe same in the structure of the liquid crystal cell and different inthe positions of the polarizing plates 11 and 26 illustrated in FIG. 1.

In transmissive display using the space of the reflective electrodes 63between the pixels 50, not all the liquid crystal molecules between thepixels switch, thereby leaving an area where no liquid crystal moleculemoves. In the normally white mode, the area where no liquid crystalmolecule moves may possibly prevent the semi-transmissive liquid crystaldisplay device 1 from displaying black sharply, thereby reducing thecontrast.

FIG. 13 illustrates movement of liquid crystal molecules between pixelsin transmissive display using a space of the reflective electrodes 63between the pixels. In FIG. 13, the liquid crystal molecules fully moveat a position A in the center of the reflective electrode 63. Bycontrast, the liquid crystal molecules move to some extent at a positionB near the reflective electrode 63 between the pixels and do not move atall at a position C in the center between the pixels.

This configuration makes the transmittance in the area in the centerbetween the pixels, at which the liquid crystal molecules do not move atall, extremely higher than that in the area of the reflective electrode63, thereby causing a leak of light. This prevents the semi-transmissiveliquid crystal display device 1 from displaying black sharply, therebyreducing the contrast.

FIG. 14 illustrates a simulation result of the transmittance between thepixels in the normally white mode. Positions A, B, and C in FIG. 14correspond to the positions A, B, and C in FIG. 13, respectively. Thesimulation result of FIG. 14 shows that the transmittance is high (e.g.,approximately 0.35) at the position C in the center between the pixelsin FIG. 13 because the liquid crystal molecules do not move at all.

For this reason, the normally black mode is preferably employed for thedisplay mode of the semi-transmissive liquid crystal display deviceaccording to the present embodiment. In the normally black mode, blackis displayed when no voltage is applied to the liquid crystal, that is,when the liquid crystal orientation is uniform. This makes it possibleto display black sharply, thereby increasing the contrast. It is notintended to exclude employment of the normally white mode.

The following describes an example of observation results of opticalcharacteristics. In the normally white mode, the white transmittance (%)is approximately 0.93, and the black transmittance (%) is approximately0.29, which provides a contrast of approximately 3. In the normallyblack mode, the white transmittance (%) is approximately 0.71, and theblack transmittance (%) is approximately 0.06, which provides a contrastof approximately 12. In other words, employment of the normally blackmode can increase the contrast approximately four times of the normallywhite mode.

(Overlapping of Color Filters)

To form the color filter 22 on the second substrate 23 facing the firstsubstrate 14 on which the TFT is formed illustrated in FIG. 1, it isnecessary to consider deviation caused when superimposing the secondsubstrate 23 on the first substrate 14 (also referred to assuperimposing deviation). If the sub-pixels 50R, 50G, and 50B arepartitioned using the black matrix BM as a light-blocking zone asillustrated in FIG. 15A, superimposing deviation significantly changesthe transmittance as illustrated in FIG. 15B. If the gap betweenadjacent black matrixes BM is increased such that the black matrix BM isarranged between the pixels 50 even when the superimposing deviationoccurs, the reflectance is reduced.

As illustrated in FIG. 15C, parts of the color filters 22R and 22G andparts of the color filters 22G and 22B are each overlapped to partitionthe sub pixels 50R, 50G, and 50B with the overlapping portions OL. Theoverlapping portion OL has low transmittance but transmits light to someextent. The use of the overlapping portion OL as the light-blocking zonecan reduce a change in the transmittance and the reflectance caused byoccurrence of the superimposing deviation as illustrated in FIG. 15Dcompared with the case where the black matrix BM is used as thelight-blocking zone.

(Scattering Layer)

A semi-transmissive liquid crystal display device 1 a illustrated inFIG. 16 includes a scattering layer 27 that scatters light to the sideof a traveling direction of light reflected by a reflective electrode 63than a liquid crystal layer 30. More specifically, the semi-transmissiveliquid crystal display device 1 a includes the scattering layer 27between a second substrate 23 and a quarter-wave plate 24. Thescattering layer 27 is an anisotropic or isotropic layer that scatterslight reflected by the reflective electrode 63 and backlight passingthrough a space 65 _(A) between pixels. A light control film (LCF), forexample, may be used for the scattering layer 27.

The scattering layer 27 is a forward scattering layer that generateslarge forward scattering and small backward scattering. The scatteringlayer 27 is an anisotropic scattering layer that scatters light incidentin a specific direction. If light is incident in the specific directionfrom the polarizing plate 26 with respect to the second substrate 23,the scattering layer 27 transmits the incident light almost withoutscattering the light, and then significantly scatters the lightreflected and returned by the reflective electrode 63.

As illustrated in FIG. 17, for example, the scattering layer 27transmits outer light L1 incident in the specific direction with respectto the second substrate 23. The scattering layer 27 scatters light L2reflected by the reflective electrode 63 in the transmitted light withina predetermined range with respect to a scattering center axis AX1. Theouter light L1 is parallel light incident on the polarizing plate 26 ofthe second substrate 23. The outer light L1 may be polarized light ornon-polarized light. As illustrated in FIG. 17, the scattering layer 27includes two types of areas (a first area 27B and a second area 27S)having different refractive indexes, for example. The scattering layer27 may have a louver structure in which a plurality of plate-like secondareas 27S are arranged at predetermined intervals in the first area 27Bas illustrated in FIG. 18. Alternatively, the scattering layer 27 mayhave a columnar structure in which columnar second areas 27Sa arearranged in the first area 27B as illustrated in FIG. 19.

The scattering layer 27 is formed of the first area 27B and the secondarea 27S extending in the thickness direction and inclined in apredetermined direction, for example. The scattering layer 27 is formedby irradiating a resin sheet that is a mixture of two or more types ofmonomers or oligomers capable of being photopolymerized and havingdifferent refractive indexes with ultraviolet rays in an obliquedirection, for example. The scattering layer 27 may have a structuredifferent from the structure described above and may be manufactured bya method different from the method described above. The scattering layer27 may be formed as a single layer or a plurality of layers. If thescattering layer 27 is formed as a plurality of layers, the layers mayhave the same structure or structures different from one another.

The scattering center axis AX1 of the scattering layer 27 preferablyextends in a main visual angle direction, for example. The scatteringcenter axis AX1 may extend in a direction different from the main visualangle direction. In both cases, the direction of the scattering centeraxis AX1 needs to be set such that the use of the scattering layer 27makes the luminance in the main visual angle direction the highest, thatis, makes the reflectance the highest because of the effect of thescattering layer 27. The “main visual angle” corresponds to a directionin which a user of the semi-transmissive liquid crystal display device 1a views an image display surface when using the semi-transmissive liquidcrystal display device 1 a. If the image display surface is formed in arectangular shape, the main visual angle corresponds to a directionorthogonal to a side closest to the user among the sides of the imagedisplay surface.

When backlight is transmitted through the space 65 _(A) between thepixels, patterning accuracy of the reflective electrode 63 orsuperimposing deviation of the second substrate 23 may possibly increasefluctuations in transmission of the backlight, for example.Specifically, forming the reflective electrode 63 with silver by a wetprocess may possibly increase the fluctuations significantly. Becausethe scattering layer 27 scatters the transmitted light, the fluctuationsare leveled advantageously.

2-5. Specific Example

The following describes a specific example of the semi-transmissiveliquid crystal display device according to the present embodiment. Inthe description below, the normally black mode is employed as thedisplay mode, and an electrically controlled birefringence (ECB) mode isemployed as an operating mode, for example. The operating mode is notlimited to the ECB mode and may be the VA mode or a fringe fieldswitching (FFS) mode, for example.

FIG. 20 is a sectional view of a sectional structure of two pixelsadjacent to each other in the row direction (X-direction) of asemi-transmissive liquid crystal display device according to an exampleof the present embodiment. In FIG. 20, components similar to those inFIG. 1 are denoted by the same reference numerals.

As illustrated in FIG. 20, a first panel unit 10 includes a polarizingplate 11, a half-wave plate 12, a quarter-wave plate 13, a firstsubstrate 14 serving as a TFT substrate, and a planarizing film 15arranged in this order from the side opposite to a liquid crystal layer30, and a reflective electrode 63 is formed on the planarizing film 15for each pixel.

The reflective electrode 63 is formed in nearly the same size as that ofa pixel in the first panel unit 10. The area of the reflective electrode63 serves as the reflective display area (reflective display portion). Aspace 65 _(A) is formed along the column direction (Y-direction) betweenreflective electrodes 63 of two pixels adjacent to each other in the rowdirection (X-direction). A space 65 _(B), which is not illustrated inthis section, is formed along the row direction between reflectiveelectrodes 63 of two pixels adjacent to each other in the columndirection as illustrated in FIG. 4.

A signal line 61 that transmits a video signal to the pixels in eachpixel column is arranged on the first substrate 14. The signal line 61is formed in the reflective display area so as not to block the space 65_(A) extending along the column direction, more preferably, not tooverlap with the space 65 _(A). A scanning line 62 (refer to FIG. 4),which is not illustrated in this section, transmits a scanning signal tothe pixels in each pixel row. The signal line 62 is formed in thereflective display area so as not to block the space 65 _(B) extendingalong the row direction, more preferably, not to overlap with the space65 ₁₃.

The spaces 65 _(A) and 65 ₁₃ of the reflective electrodes 63 between thepixels with which the signal line 61 and the scanning line 62 do notoverlap are used as the transmissive display area. The pixel structureaccording to the present example is a single gap structure in which thereflective display area and the transmissive display area have the samethickness of the liquid crystal layer 30, that is, the same cell gap.

A second panel unit 20 faces the first panel unit 10 with the liquidcrystal layer 30 interposed therebetween. The second panel unit 20includes a transparent electrode 21, a color filter 22, a secondsubstrate 23, a quarter-wave plate 24, a half-wave plate 25, and apolarizing plate 26 arranged in this order from the liquid crystal layer30 side. FIG. 20 illustrates pixel structures of two pixels adjacent toeach other in the row direction, that is, a sub-pixel R that displaysred and a sub-pixel G that displays green, for example.

FIG. 21A and FIG. 21B illustrate an example of optical design of anormally black ECB mode in the single-gap structure. FIG. 21A and FIG.21B illustrate axial directions of components of the first panel unit10, the liquid crystal cell (liquid crystal layer 30), and components ofthe second panel unit 20. Specifically, FIG. 21B illustrates the axialdirections of the first panel unit 10, including an absorption axialdirection of the polarizing plate 11, an extension axial direction ofthe half-wave plate 12, and an extension axial direction of thequarter-wave plate 14. FIG. 21A illustrates the axial directions ofsecond panel unit 20, including rubbing directions of the liquid crystalcell on the TFT substrate side and the CF substrate side, an extensionaxial direction of the quarter-wave plate 24, an extension axialdirection of the half-wave plate 25, and an absorption axial directionof the polarizing plate 26.

In FIGS. 21A and 21B, each numerical value represents the angle of eachaxial direction and a phase difference (retardation). The phasedifference is a numerical value obtained by converting the phasedifference into a wavelength in a case where light at a wavelength of550 nm is incident on each component of the first panel unit 10 and thesecond panel unit 20. While the explanation has been made of the singlegap structure as a specific example, the pixel structure may be amulti-gap structure in which the reflective display area and thetransmissive display area have different cell gaps as illustrated inFIG. 22.

In the multi-gap structure, a groove needs to be formed at the space 65_(A) (65 _(B)) of the reflective electrodes 63 between pixels so as toform a difference in level between the reflective display area and thetransmissive display area as illustrated in FIG. 22. This increases thenumber of processes compared with the single gap structure. Because thesingle gap structure can be formed by fewer processes than those of themulti-gap structure, the single gap structure is preferably employed interms of the process.

FIG. 23 and FIG. 24 illustrate calculation results of spectra in thereflective display area and the transmissive display area obtained whena voltage is turned ON or a voltage is turned OFF to the upper and lowerelectrodes of the counter electrode (transparent electrode 21) and thepixel electrode (reflective electrode 63) in the optical design (singlegap structure) illustrated in FIG. 21A and FIG. 21B. “A voltage isturned ON” means a state where a voltage is applied between the upperand lower electrodes, whereas “a voltage is turned OFF” means a statewhere no voltage is applied between the upper and lower electrodes.

FIG. 23 illustrates a calculation result of a spectrum of thereflectance in the reflective display area. FIG. 24 illustrates acalculation result of a spectrum of the transmittance in thetransmissive display area. These calculation results is made based onnot the reproduction of the electric field distribution between pixelsbut a state where the electric field generated by the upper and lowerelectrodes completely affects the liquid crystal molecules. Because thesemi-transmissive liquid crystal display device according to the presentexample has the single gap structure, the phase difference is small inthe transmissive display area unlike a typical semi-transmissive liquidcrystal display device having the multi-gap structure. As a result, thesemi-transmissive liquid crystal display device according to the presentexample has low transmittance in the transmissive display.

3. MODIFICATIONS

The embodiments described above have a wiring structure formed of thesignal line 61 and the scanning line 62 each arranged in a linear stripepattern. The signal line 61 traverses the space 65 _(B) extending in therow direction through a position around the center of pixels, whereasthe scanning line 62 traverses the space 65 _(A) extending in the columndirection through a position around the internal position of pixels(refer to FIG. 4). The wiring structure of the signal line 61 and thescanning line 62 described above is given just as an example, and thewiring structure is not limited thereto.

As illustrated in FIG. 25, for example, the signal line 61 and thescanning line 62 may be formed into bent and meandering wiring with thefollowing wiring structure. The signal line 61 is arranged so as to passthrough an intersection 65 _(c) between the space 65 _(A) formed alongthe column direction and the space 65 _(B) formed along the rowdirection at a space between pixels adjacent to each other in the rowdirection. Specifically, the signal line 61 is arranged such that a bentportion 61A is positioned at the intersection 65 _(c). The scanning line62 is arranged so as to pass through the intersection 65 c between thespace 65 _(B) formed along the row direction and the space 65 _(A)formed along the column direction at a space between pixels adjacent toeach other in the column direction. Specifically, the scanning line 62is arranged such that a bent portion 62A is positioned at theintersection 65 _(c).

As described above with reference to FIG. 13 and FIG. 14, the liquidcrystal molecules do not move at all at the portion C in the centerbetween the pixels. Therefore, the center of the intersection 65 _(c)between the space 65 _(A) formed along the column direction and thespace 65 _(B) formed along the row direction most negatively affectstransmissive display. Passing the signal line 61 and the scanning line62 not through positions around the respective center of the pixels inthe spaces 65 _(A) and 65 _(B) but through the intersection 65 _(c) likein the wiring structure according to the modification can achieveexcellent transmissive display compared with the former wiringstructure.

4. ELECTRONIC APPARATUSES

The semi-transmissive liquid crystal display device according to thepresent disclosure is applicable to a display unit (a display device) ofany types of electronic apparatuses that displays a video signalreceived by the electronic apparatuses or a video signal generated inthe electronic apparatuses as an image or video.

The semi-transmissive liquid crystal display device according to thepresent disclosure is preferably applied to a display unit (a displaydevice) of mobile devices frequently used outdoors among any types ofelectronic apparatuses. Examples of the mobile devices include, but arenot limited to, mobile information devices, such as digital cameras,video cameras, personal digital assistants (PDAs), gaming devices,portable personal computers, and electronic book readers, and mobilecommunication devices, such as mobile phones.

As is clear from the description of the embodiments, thesemi-transmissive liquid crystal display device according to the presentdisclosure can carry out transmissive display while maintainingreflective display performance equivalent to that of a reflectivedisplay device. The semi-transmissive liquid crystal display device canfully enjoy the characteristics of a reflective liquid crystal displaydevice in that less power consumption is required and the screen is easyto read under light environment. Application of the semi-transmissiveliquid crystal display device according to the present disclosure to adisplay unit of any types of electronic apparatuses, specifically, ofmobile devices can contribute significantly to low power consumption ofthe mobile devices.

The following describes electronic apparatuses provided with thesemi-transmissive liquid crystal display device 1 or 1 a according tothe present disclosure as a display unit, that is, specific examples ofan electronic apparatus according to the present disclosure.

FIG. 26A is a perspective view of an appearance of a digital cameraviewed from the front, to which the present disclosure is applied. FIG.26B is a perspective view of an appearance of the digital camera viewedfrom the back. The digital camera according to the present exampleincludes a light-emitting unit 111 that outputs flashlight, a displayunit 112, a menu switch 113, and a shutter button 114. The digitalcamera is manufactured by applying the semi-transmissive liquid crystaldisplay device 1 or 1 a according to the present disclosure to thedisplay unit 112.

FIG. 27 is a perspective view of an appearance of a video camera towhich the present disclosure is applied. The video camera according tothe present example includes a main body 131, a lens 132 arranged on theside facing the front to capture a subject, a start/stop switch 133 usedin capturing, and a display unit 134. The video camera is manufacturedby applying the semi-transmissive liquid crystal display device 1 or 1 aaccording to the present disclosure to the display unit 134.

FIG. 28 is a perspective view of an appearance of a notebook personalcomputer to which the present disclosure is applied. The notebookpersonal computer according to the present example includes a main body121, a keyboard 122 operated when inputting characters and the like, anda display unit 123 that displays an image. The notebook personalcomputer is manufactured by applying the semi-transmissive liquidcrystal display device 1 or 1 a according to the present disclosure tothe display unit 123.

FIG. 29A to FIG. 29G are views of an appearance of a mobilecommunication device, such as a mobile phone, to which the presentdisclosure is applied. FIG. 29A is a front view of the mobile phone inan unfolded state, and FIG. 29B is a side view. FIG. 29C is a front viewof the mobile phone in a folded state, FIG. 29D is a left side view,FIG. 29E is a right side view, FIG. 29F is a top view, and FIG. 29G is abottom view.

The mobile phone according to the example includes an upper housing 141,a lower housing 142, a connection (a hinge in this example) 143, adisplay device 144, a sub-display device 145, a picture light 146, and acamera 147. The mobile phone according to the present example ismanufactured by applying the semi-transmissive liquid crystal displaydevice 1 or 1 a according to the present disclosure to the displaydevice 144 and the sub-display device 145.

According to one aspect of the present disclosure, transmissive displaycan be achieved while maintaining reflective display performanceequivalent to that of a reflective display device by carrying out thetransmissive display with a space between pixels of reflectiveelectrodes.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

The invention is claimed as follows:
 1. A semi-transmissive liquidcrystal display device comprising: a plurality of pixels arranged in amatrix; a plurality of reflective electrode groups provided for each ofthe pixels, each of the reflective electrode groups including one ormore reflective electrodes, with a combination of the areas of thereflective electrode groups being used to perform area coveragemodulation using n bits, where n is an integer equal to or more than 2,each reflective electrode group corresponding to one of the n bits, thereflective electrode groups being configured such that a ratio of thesum of the perimeters of the reflective electrodes in each reflectiveelectrode group corresponding to each bit of the n bits satisfies 1:2: .. . :2^(n−1), a counter electrode facing the plurality of reflectiveelectrode groups; and a liquid crystal layer provided between thereflective electrode groups and the counter electrode, wherein thesemi-transmissive liquid crystal display device is configured to carryout reflective display using the reflective electrodes, and carry outtransmissive display using at least a space of the reflective electrodesbetween the pixels, wherein the reflective electrodes are arranged suchthat luminance and gradation change in proportion to each other, andwherein a gap between reflective electrodes adjacent to each other inone of the pixels is larger than a gap between reflective electrodes oftwo pixels adjacent to each other in a column direction.
 2. Thesemi-transmissive liquid crystal display device according to claim 1,wherein the reflective electrodes corresponding to a bit higher than theleast significant bit are arranged symmetrically with respect to one ormore of the reflective electrodes corresponding to the least significantbit.
 3. The semi-transmissive liquid crystal display device according toclaim 1, wherein the reflective electrodes include a first reflectiveelectrode, a second reflective electrode, and a third reflectiveelectrode, the reflective electrode groups being configured to performthe area coverage modulation by using 2 bits with an area ratio of 2:1with a combination of the areas of the first and second reflectiveelectrodes with the third reflective electrode, and the first and secondreflective electrodes are arranged adjacent to each other andelectrically connected on a same plane, and first reflective electrodeis adjacent to the third reflective electrode.
 4. The semi-transmissiveliquid crystal display device according to claim 3, further comprising aconductor formed of a same material as that of the first and secondreflective electrodes, the conductor electrically connecting the tworeflective electrodes on the plane, wherein the first and secondreflective electrodes and the conductor are integrally formed.
 5. Thesemi-transmissive liquid crystal display device according claim 1,wherein the reflective electrodes have a same shape and a same size. 6.The semi-transmissive liquid crystal display device according to 1,wherein two or more of the reflective electrodes corresponding to thesame bit are electrically connected to one another.
 7. Thesemi-transmissive liquid crystal display device according to claim 1,wherein a gap between a reflective electrode corresponding to a lowerbit and an adjacent reflective electrode thereof in one of the pixels islarger than a gap between a reflective electrode corresponding to ahigher bit and an adjacent reflective electrode thereof in the pixel. 8.The semi-transmissive liquid crystal display device according to claim1, wherein parts of color filters included in the pixels adjacent toeach other in a row direction overlap with each other.
 9. Thesemi-transmissive liquid crystal display device according to claim 1,further comprising a scattering layer for scattering light to a side ofa traveling direction of light reflected by the reflective electrodethan the liquid crystal layer.
 10. The semi-transmissive liquid crystaldisplay device according to claim 1, wherein the semi-transmissiveliquid crystal display device has a display mode of a normally blackmode.
 11. The semi-transmissive liquid crystal display device accordingto claim 1, wherein the pixels have a memory function.
 12. Thesemi-transmissive liquid crystal display device according to claim 11,wherein the pixels comprise a memory that stores therein data.
 13. Thesemi-transmissive liquid crystal display device according to claim 12,wherein the pixels are provided with memory liquid crystal.
 14. Asemi-transmissive liquid crystal display device comprising: a pluralityof pixels arranged in a matrix; a plurality of reflective electrodegroups provided for each of the pixels, each of the reflective electrodegroups including one or more reflective electrodes, with a combinationof the areas of the reflective electrode groups being used to performarea coverage modulation using n bits, where n is an integer equal to ormore than 2, each reflective electrode group corresponding to one of then bits, the reflective electrode groups being configured such that aratio of the sum of the perimeters of the reflective electrodes in eachreflective electrode group corresponding to each bit of the n bitssatisfies 1:2: . . . :2^(n−1) in an opening of the pixel, a counterelectrode facing the plurality of reflective electrode groups; and aliquid crystal layer provided between the reflective electrode groupsand the counter electrode, wherein the semi-transmissive liquid crystaldisplay device is configured to carry out reflective display using thereflective electrodes, and carry out transmissive display using at leasta space of the reflective electrodes between the pixels, wherein thereflective electrodes are arranged such that luminance and gradationchange in proportion to each other, and wherein a gap between reflectiveelectrodes adjacent to each other in one of the pixels is larger than agap between reflective electrodes of two pixels adjacent to each otherin a column direction.